The present invention relates to a method of producing coated paper. More particularly, the invention relates to a method of efficiently producing high grade coated paper having excellent printability such as good ink gloss and ink smoothness, by the utilization of a novel blade coater.
In a method of producing coated paper in which coating composition is applied to a moving web of base paper, the role of a blade coater has become increasingly more important as the solids content of the coating compositions is increased and operating speeds are increased. A blade coater can generally facilitate a uniform control of coating weight, provide excellent runnability of high solids coating compositions and produce coated paper having relatively good smoothness and gloss.
However, the conventional application of coating by the use of blade coaters has encountered problems related to the increase in the solids content of the coating compositions and in the viscosity of such and further in the trend toward higher coating speeds. If a coating composition having a high solids content is applied at a high speed, the coating weight is liable to increase. To prevent the increase of the coating weight, it is necessary to further increase the pressure applied to the blade in order to wipe or scrape off the excess. As a result, the smoothness of the coated paper is lost. Particularly, it is difficult to obtain high grade printing paper which needs good ink gloss and ink smoothness. Further, the solids content of the coating layer increases and its water content decreases during the dwell time, that is, the time interval between the time when the coating composition first contacts the base paper and the time when the excess coating is wiped or scraped off, with the result that defects such as streaks and scratches in the coating are liable to occur.
Japanese Patent Publications No. 29471/1968 and No. 40460/1973 disclose coating methods for obtaining a relatively smooth coated layer, particularly a coated layer having a good profile across the width of the base paper, in which the excess coating is scraped off by a part of the curved surface of a bent blade. However, these methods have the disadvantages that it is difficult to apply a uniform coating weight and difficult to prevent defects such as streaks and scratches in the application of coating compositions having high solids content or in the high speed application of the coatings because the dwell time of the coating composition is long.
A coating method for shortening the swell time is proposed in Japanese Patent Laid-Open Publication No. 84770/1982. However, while this method can suppress the occurrence of defects such as streaks and scratches to some degree, it is still difficult to control the coating weight, with the result that uneven coating and decrease in the smoothness of the resulting coated paper cannot be avoided.